The present invention relates to a golf ball in which the flight performance has been improved by designing the dimples and lands formed on the surface of the ball in unique shapes.
In golf balls, it is well-known that, in order for a launched ball to travel a long distance, it is important for the ball itself to have a high rebound and for the air resistance during flight to be reduced by dimples arranged on the surface of the ball. Various methods for arranging the dimples uniformly and in the highest possible density in order to reduce air resistance have been disclosed.
As shown in FIGS. 18 and 19, it is generally common for the dimples D used on a golf ball to be in the shape of circular recesses as seen from above. Attempts to arrange circular dimples to a high density, such as by making the width of the land dividing two neighboring dimples as close to zero as possible, result in the formation of triangular or quandrangular lands t of a given size in areas surrounded by three or four of the arranged dimples. At the same time, because it is essential to arrange the dimples as uniformly as possible on the spherical surface of the ball, some concessions have had to be made when it comes to the density in which circular dimples are arranged.
In light of the above, to arrange the dimples uniformly and to a high density, from two to five types of dimples of differing diameter are disposed in such a way as to give the spherical surface of the ball the appearance of a polyhedron such as a regular octahedron or a regular icosahedron.
However, so long as circular dimples are used, the practical upper limit in the dimple surface coverage, defined as the ratio of the sum of the individual dimple surface areas to the total surface area of the spherical surface, is about 75% (that is, the surface coverage represented by the land surface areas collectively is about 25%).
In this connection, numerous disclosures have been made recently which attempt to increase the aerodynamic performance of the ball, both by using dimples having non-circular surface shapes, such as elliptical, teardrop or polygonal shapes, and in particular by combining such dimples with circular dimples to create a unique dimple configuration on the ball as a whole, and also by making the surface area of the lands on the ball surface as small as possible. Of these, the present applicant earlier disclosed JP-A 2006-095281 and JP-A 2005-305152.
As shown in FIGS. 16 and 17, the golf balls in the foregoing disclosures, along with having numerous circular dimples D1 formed on the ball surface, have circular ring-like lands 51 formed along edges of the circular dimples D1, and additionally have rectilinear lands 52 formed so as to bridge between different circular ring-like lands 51, 51. In addition, non-circular dimples D2 are formed between three or four mutually neighboring circular dimples D1 in such a way as to be surrounded by the lands.
The foregoing golf balls do enable the land surface area to be made smaller than in conventional golf balls. However, in order to considerably enhance the flight performance by reducing air resistance through additional dimple effects, there remains room for further improvement.